1. Field of the Invention
The present invention relates to an inverter device capable of supplying an alternating current (AC) power to a cold cathode fluorescent lamp (CCFL).
2. Description of Related Art
In a thin film transistor (TFT) LCD or other LCD display panel, a power supplied to a backlight source therein is mainly for allowing an inverter circuit to achieve energy conversion and a cold cathode fluorescent lamp (CCFL) to achieve light emitting. According to circuit topologies, the prior inverter circuits used to converse a direct current (DC) power into an alternating current (AC) power are generally categorized into half-bridge inverter circuits, full-bridge inverter circuits, Clark converters and the like.
Referring to FIG. 1, a schematic diagram of the prior Clark converter circuit is depicted therein. As shown in FIG. 1, the Clark converter comprises a transformer 401 having a center tap connected to a positive terminal of a DC power 408 through an inductor 403. Meanwhile, two input terminals of the transformer 401 are connected to a negative terminal of the DC power source 408 through switches 405,406, respectively. In the Clark converter circuit, it is operated based on the following principle. A control unit 407 is provided to control the switches 405,406 alternatively. Based on the switching operations of the switches 405,406, the DC power source 408 may transmit a DC power to the transformer 401 through the inductor 403, in which the DC power transmitted is conversed by means of the transformer 401 to provide a desired DC power for use of the CCFL to emit a light.
In the above, the switches 405,406 may also be switched by a self-excited driving manner. Further, an outputted power of the Clark converter circuit vanes with the inputted DC power since the circuit itself does not provide any power regulation function with respect to the outputted power.
Referring to FIG. 2, a schematic circuit diagram of the prior full-bridge converter is depicted therein. In the circuit, a transformer 501 is provided and a former-stage circuit at a primary side thereof and a latter circuit-stage at a secondary side thereof are separated by the transformer 501. The former-stage circuit at the primary side comprises four switches 503,504,505,506, a full-bridge control module 509, a DC block capacitor 510 and the like. The latter-stage circuit at the secondary side comprises a load. The full-bridge control module 509 outputs four control signals to control four switches (503,504,505,506), respectively, so that the DC power source 507 supplies a voltage to the transformer 501 through a capacitor 510. Further, the voltage outputted from the transformer 501 is boosted at the secondary winding and inputted to the former-stage circuit corresponding thereto in such a manner that the load is properly driven. In this full-bridge converter circuit, the drive stage for the switches 503,505 at the high voltage side of the transformer 501 has to be provided with a voltage shift circuit. However, such voltage shift circuit introduces an additional transmission delay, making different of its timings compared with those of the switches 504,506 at the low voltage side of the transformer 501. As such, a non-symmetric input voltage V1 is generated, resulting in magnetic saturation of the transformer 501. To prevent the magnetic saturation, a DC block capacitor 510 is generally connected at the primary side of the transformer 501.